粉末冶金高温合金异常大晶粒形成机理及影响机制的多尺度研究

Powder metallurgy superalloy turbine disk (PMSTD) is the key hot rotating components of advanced aeroengine. However, abnormally large grains formed during the fabrication of PMSTD would significantly reduce performance and life of PMSTD, which would easily cause fatigue crack initiation and propagation and lead to failure. Currently, the formation and influence mechanisms of abnormally large grain are not fully understood, which severely restrict the development of fabricating high-performance PMSTD. The current project aimed at this common problem and will focus on the following research based on the high throughput sample and with the help of in-situ synchrotron radiation X-ray, large-scale characterization technique EBSD and numerical simulation method: 1) The deformation mechanism microstructure and energy of powder metallurgy superalloy are high-throughput and precisely investigated. 2) The formation and influence mechanisms are investigated in multiscale and visualization by focusing on studying the evolution of micro-structure and stored energy in grain-scale. 3) Energy, structure, crystallography conditions and predicition models for abnormally large grain are quantificationally studied in details. Finally, revealing the scientific formation mechanism of abnormally large grain in multiscale, and making a breakthrough of technical bottleneck and scientific problem. After the project is finished succefully, the new principle, technique, method with proprietary intellectual property rights for regulating the microstrcture of new-designed powder metallurgy superalloy during fabrication will be formed.

粉末冶金高温合金涡轮盘是先进航空发动机的关键热转动部件。然而，涡轮盘制备过程中形成的异常大晶粒是降低涡轮盘疲劳性能和寿命的重要顽疾，其极易引起疲劳裂纹萌生并扩展，致使涡轮盘发生失效。当前，关于异常大晶粒的形成机理及影响机制尚未完全明确，严重制约了高性能粉末冶金高温合金涡轮盘制备技术的发展。本项目针对该共性问题，基于高通量试样，借助同步辐射X射线、大面积EBSD表征技术及相场模拟方法，拟重点开展以下研究：1）变形机理、显微结构和储能状态的高通量、精细化研究；2）聚焦晶粒尺度下结构与储能的动态演变研究，多尺度研究异常大晶粒形成微观机理及影响机制；3）异常大晶粒形成的能量、组织、晶体学条件及预测模型的定量研究。最终，多尺度揭示异常大晶粒形成的科学原理，突破先进航空发动机粉末涡轮盘制造过程的技术瓶颈和科学问题，形成具有自主知识产权的新型高性能粉末高温合金制备及组织调控新原理、新技术和新方法。

本项目针对航空发动机用粉末高温合金制备过程的顽疾----异常大晶粒为主要研究内涵，借助有限元模拟、热模拟与超精细显微组织表征方法，系统、高通量探究了热机械处理过程的变形与热处理工艺耦合作用下的显微组织演化规律、变形机理；多尺度研究了异常大晶粒的形成机理与影响机制。项目研究发现，常晶粒长大主要源于热处理过程中，再结晶形核受限，部分形核的再结晶晶核发生迅速长大，造成异常大晶粒的形成。合金大变形区域发生相对均匀的动态再结晶行为，可促进后续热处理过程中静态再结晶形核均匀，晶核均匀地长大直至相互碰撞，因而形成均匀细小的组织；具有应变梯度分布的形变区域，其动态再结晶形核受阻，形成储能分布不均的再结晶组织，在后续热处理过程发生局部静态再结晶后迅速长大，出现异常大晶粒。此外，项目研究表明，二道次形变可有效细化合金晶粒组织。经高应变速率变形后，一道次结束后，体系位错密度及应变储能较大，在保温阶段能促使静态再结晶的发生及退火孪晶的形成。静态再结晶的发生，使材料内部位错密度及应变储能下降，在细化晶粒的同时，降低二道次的应力；而孪晶的形成，则有利于促进二道次变形过程以孪生形核为形核机制的动态再结晶的发生，从而进一步细化晶粒。项目研究成果将为粉末高温合金和其他相关合金的工艺设计、异常大晶粒调控及性能优化提供有力的理论依据和实际参考。